linux-kernel - Re: [PATCH v2 2/2] tty: check tcsetpgrp p is a process group

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Date:	Sun, 28 Jun 2015 21:27:07 -0400
From:	Patrick Donnelly <batrick@...bytes.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] tty: check tcsetpgrp p is a process group

On Sun, Jun 28, 2015 at 12:07 PM, Peter Hurley <peter@...leysoftware.com> wrote:
> On 06/27/2015 08:51 PM, Patrick Donnelly wrote:
>> This fixes a bug where a process can set the foreground process group to its
>> pid even if its pid is not a valid pgrp.
>>
>> Signed-off-by: Patrick Donnelly <batrick@...bytes.com>
>> ---
>>  drivers/tty/tty_io.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
>> index fbb55db..01b4769 100644
>> --- a/drivers/tty/tty_io.c
>> +++ b/drivers/tty/tty_io.c
>> @@ -2579,6 +2579,9 @@ static int tiocspgrp(struct tty_struct *tty, struct tty_struct *real_tty, pid_t
>>       retval = -ESRCH;
>>       if (!pgrp)
>>               goto out_unlock;
>> +     retval = -EINVAL;
>> +     if (!pid_task(pgrp, PIDTYPE_PGID))
>> +             goto out_unlock;
>
> This change implies that the sequence in session_of_pgrp() that specifically
> checks for pid_task(pgrp, PIDTYPE_PGID) == NULL is not doing anything
> useful. However, that hypothesis is directly contradicted by the
> comment above session_of_pgrp()
>
> "* This checks not only the pgrp, but falls back on the pid if no
>  * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
>  * without this..."
>
> Regards,
> Peter Hurley
>
>>       retval = -EPERM;
>>       if (session_of_pgrp(pgrp) != task_session(current))
>>               goto out_unlock;
>>

Ah, missed that. Good catch! I guess this patch is no good since it
was already accounted for and it breaks gdb.

-- 
Patrick Donnelly
--
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